Shear-Driven Assembly of Nanorods in Polymer Nanocomposites

Polymer nanocomposites (PNCs) are a diverse class of soft materials which comprise a polymer matrix with nanoparticle fillers. Understanding the nonequilibrium structure and dynamics of PNCs during processing flows is necessary to enable the fabrication of anisotropic, soft materials with tailorable mechanical, electrical, optical, and thermal properties. In this talk, we describe coarse-grained molecular dynamics simulations of thin nanorods in entangled polymer melts under simple shear flow. Simulations show that nanorods undergo shear-driven alignment and aggregate to form bundles. Our simulations systematically map out a nonequilibrium phase diagram for nanorod alignment and assembly as a function of shear rate, matrix chain length, and nanorod length and volume fraction. We also explore the effect of nanorods on shear banding and how incorporating nanorods into melts alters their nonlinear viscosity. Our results highlight how subtle differences in nanorod design, matrix chain length, and flow conditions can significantly alter PNC structure and rheological properties, creating new design opportunities for engineered nanocomposites.